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sprinkles08
sprinkles08, ASE Certified Technician
Category: UK Car
Satisfied Customers: 21572
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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Subaru LGT: 05 Legacy GT. Random idle drop at traffic lights,

Customer Question

05 Legacy GT. Random idle drop at traffic lights, drive throughs. Smooth then drops, low stumbly idle, sometimes stalls. Not to "lead" you but seems like vac leak behavior but why random? Injector?
Took to dealer, cleaned TB, not solved, took to dealer they reflashed, not solved, took to dealer, disconnected batt for long time to drain all, reconnected started to set idle said fixed for sure, no, not fixed. It will go days without doing then suddenly do it. Idle quality in general is not 100%. related to emissions purge cycle?
Submitted: 1 year ago.
Category: UK Car
Expert:  sprinkles08 replied 1 year ago.
Hello and welcome to JustAnswer!

It's possible that the problem is happening when the purge solenoid comes on but if that's what is killing the engine then there is liquid fuel in the evap system for some reason. You can try unpluging the purge solenoid and see if it changes anything.

I'm wondering if you may have a weak upstream oxygen sensor heater. The sensors contain internal heaters to bring them up to temperature faster and keep them there. If a sensor cools back off enough at idle because of a weak heater than it will take fuel away. This can be seen on a scan tool while the problem is happening or you could try unplugging the sensor to see if it makes a difference.
Customer: replied 1 year ago.

Thank you for your response. The last time it killed the engine the CEL came on. The wife mentioned that she had recently filled the tank so I asked her to tighten the gas cap. Before long the CEL went off and the car was nearly normal (I say nearly but still 50/100 rpm lower then it used to be before these issues).

Yesterday it did it again at idle, sudden rough very low idle, then died. Took more cranks than usual to start, put it in gear (auto), died again, CEL came on. Wife was able to get it drive home fairly normally but refuses to drive again, CEL still on. It seems I need to help the dealer work a little harder in researching the issue. No offense to dealer techs but the service management personnel treat the wife "like a girl" "Don't worry little lady, we fixed it, we know what we're doing", not fixed. I'm on an assignment away from home so it's difficult for me to diagnose, it did it to me once while home recently but it did not actually kill the motor, but it happens suddenly when it does it.

BTW, like your avatar, thats a P-40. (I'm a pilot) Eric

Expert:  sprinkles08 replied 1 year ago.
The P-40 is one of my favorites!
Do you know what fault codes are setting?

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